Substrate etch

ABSTRACT

An example provides a method including sputtering a metal catalyst onto a substrate, exposing the substrate to a solution that reacts with the metal catalyst to form a plurality of pores in the substrate, and etching the substrate to remove the plurality of pores to form a recess in the substrate.

BACKGROUND

A number of devices may be implemented with recesses or voids (such as,e.g., a chamber or channel) in a substrate. Micro-electrical-mechanicalsystems (MEMS) devices, for example, may include air chambers to housecomponents and/or to provide functionality to the devices. Printheads,which sometimes may be MEMS-based, may include firing chambers, ink feedslots, or ink channels.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description section references the drawings, wherein:

FIG. 1 is a flow diagram of an example method for etching a substrate;

FIGS. 2-5 illustrate sectional views of a substrate at various stages ofan example method for etching the substrate; and

FIGS. 6-8 illustrate sectional views of a substrate at various stages ofanother example method for etching the substrate;

all in which various examples may be implemented.

Certain examples are shown in the above-identified figures and describedin detail below. The figures are not necessarily to scale, and variousfeatures and views of the figures may be shown exaggerated in scale orin schematic for clarity and/or conciseness.

DETAILED DESCRIPTION OF EMBODIMENTS

Many devices are fabricated to include recesses or other openings (e.g.,chambers, channels, voids, etc.). Micro-electrical-mechanical systems(MEMS) devices, for example, may include chambers to house componentsand/or to provide functionality to the devices. Printheads may includefiring chambers, ink feed slots, or ink channels, and sometimes may befabricated using MEMS technology. In some cases, recesses or voids maybe formed in a layer and the layer may be bonded with at least one otherlayer to form a device.

Bulk micromachining of substrates may be performed using dry or wetetching processes. Bulk dry etch processes, however, may be lengthy asthese processes are commonly performed on a one-wafer-run basis. In somewet etch operations, trenches with sloped, rather than vertical,sidewalls may be formed.

Described herein are implementations of methods for etching a substrate.In some examples, a method for etching a substrate may include providinga substrate including an area having a plurality of pores and etchingthe area of the substrate to remove the plurality of pores to form arecess in the substrate. In various implementations, etching a substrateincluding a plurality of pores may facilitate bulk etching of thesubstrate when fabricating a device, such as, for example, a MEMSdevice, a printhead, or another device, using the substrate.

An example method 100 for etching a substrate is illustrated in FIG. 1.Processing for the method 100 may begin or proceed with sputtering ametal catalyst onto a substrate, at block 102. In variousimplementations, sputtering metal catalyst onto the substrate mayprovide a discontinuous layer of the metal catalyst having asubstantially uniform distribution of a plurality of islands of themetal catalyst across the substrate, with a substantially narrow sizedistribution as compared to forming particles on a substrate viasolution deposition of pre-fabricated nano-spheres on the surface of thesubstrate. In some implementations, the layer of the metal catalyst maycomprise a thin film of the metal catalyst with substantial open areas,such as, for example, a “net” morphology. In some implementations, thelayer of the metal catalyst may comprise a continuous layer of the metalcatalyst.

In various implementations, a distribution of islands of the metalcatalyst may be formed on the substrate by using shortened depositiontimes at a power dosage such that a discontinuous layer of metal isformed on the substrate rather than a continuous film. For example,islands of the metal catalyst may be sputtered at a power in a range ofabout 50 W to about 200 W for a time in a range of about 5 seconds toabout 60 seconds. The temperature during sputtering may in a range ofabout 30° C. to about 250° C. The pressure during sputtering may be in arange of about 1⁻² Torr to about 1⁻⁷ Torr.

The substrate may comprise one layer or multiple layers. For example,the substrate may comprise at least one layer of silicon, silicongermanium, a nitride, an oxide, a polymer, a ceramic, a metal, a groupIII-V material, a combination thereof, etc. In at least someimplementations, the substrate may comprise silicon or silicon with atleast one other layer thereon. In various implementations, the substratemay comprise any material suitable for forming a device, such as, forexample, a MEMS device, a printhead, or another device. Various othersubstrate materials may be possible within the scope of the presentdisclosure.

It is noted that although various drawings referenced herein may depictthe substrate as a single unitary layer, it should be understood thatthe substrate may in fact comprise multiple substrate layers and thatany reference to a surface of the substrate may mean a surface of asubstrate that comprises multiple layers. In some implementations, thesubstrate may comprise multiple substrates bonded together, and themultiple substrates may comprise the same crystal orientations ordifferent crystal orientations.

The metal may comprise any metal that reacts with the solutionsdescribed herein to etch the substrate via metal-assisted chemicaletching. For example, in various implementations, the metal may comprisea metal catalyst that reacts with a solution of hydrofluoric acid withhydrogen peroxide or nitric acid, or both, to etch the substrate.Examples of suitable metals may include, but are not limited to, gold,silver, platinum, ruthenium, platinum, palladium, molybdenum, chromium,copper, tantalum, titanium, tungsten, and alloys thereof.

The method 100 may proceed to block 104 by etching the substrate using asolution that reacts with the metal layer to form a plurality of poresin the substrate. In various implementations, the solution may comprisehydrogen peroxide and/or nitric acid with hydrofluoric acid and water,and the etching operation may comprise a metal-assisted chemical etchprocess in which the metal is a catalyst, and the substrate surface actsas an anode and the metal acts as the cathode. The metal may catalyzethe reduction of hydrogen peroxide or nitric acid, which may result in aflow of electrons from the anode to the cathode and the “sinking” of themetal into the substrate to anisotropically etch the substrate. Invarious implementations, an etch rate using the solution and the metalcatalyst may be 5 μm per minute or greater. In various implementations,nitric acid added to a solution of hydrogen peroxide, hydrofluoric acid,and water may add isotrophy to the etch to dissolve the porous substrateas it is created. In some of these implementations, the amount of thenitric acid may control, at least in part, lateral etching of areas nearthe surface of the substrate while the ratio of the nitric acid to thehydrogen peroxide may control, at least in part, the sidewall profile.

Etching of the substrate by the solution may be performed at ambienttemperature or another suitable temperature. Increasing temperature may,in some cases, increase or otherwise impact the etch rate. In someimplementations, the etching of the substrate by the solution may beperformed under agitation or in a still bath. The solution may beformulated by any concentration to provide a particular etch rate.Likewise, the ratio of hydrogen peroxide to hydrofluoric acid to wateror nitric acid to hydrofluoric acid to water may depend on theparticular etch rate, and may vary during the etch operation. In variousimplementations, the etching may be performed under illumination with UVor optical wavelengths, which may increase or other increase efficiencyof the etch.

After etching the substrate at block 104, the method 100 may proceed toblock 106 by etching the substrate to remove the plurality of pores toform a recess in the substrate. In various implementations, forming therecess in the substrate including the plurality of pores may allow theetch to proceed at a faster rate as compared to etching a substratewithout pores. The substrate may be etched to remove the plurality ofpores using a wet etch with an etchant such as, but not limited to,tetra-methyl ammonium hydroxide or potassium hydroxide. In otherimplementations, the substrate may be etched to remove the plurality ofpores using a dry etch.

The recess may comprise any opening in the substrate. For example, therecess may comprise a trench, a blind hole, a through-hole, etc. Invarious implementations, multiple recesses may be formed in thesubstrate at different locations of the substrate. In variousimplementations, the recess(es) may form, at least in part, a MEMSdevice, a printhead device, or another device. In variousimplementations, a recess may have a width of at least 1 μm. In some ofthese implementations, the recess may have a width in a range of about10 μm to about 20 μm.

Understanding of the various methods for etching a substrate asdescribed herein may be facilitated with reference to FIGS. 2-8, whichdescribe various operations for etching a substrate by way of sectionalviews of the substrate at various stages of the methods. It should benoted that various operations discussed and/or illustrated may begenerally referred to as multiple discrete operations in turn to help inunderstanding various implementations. The order of description shouldnot be construed to imply that these operations are order dependent,unless explicitly stated. Moreover, some implementations may includemore or fewer operations than may be described.

Turning now to FIG. 2, a method for etching a substrate 210, inaccordance with various implementations, may begin or proceed withproviding a substrate 210 and sputtering a metal catalyst layer 218 ontothe surface 216 of the substrate 210, and then etching the substrate 210using a solution that reacts with the metal catalyst layer 218 to form aplurality of pores 220 in the substrate 210, as shown in FIG. 3.

After etching the substrate 210 to form the plurality of pores 220, thesubstrate 210 may be etched to remove at least some of the plurality ofpores 220 to form at least one recess 222 in the substrate 210, as shownin FIG. 4. In various implementations, all or fewer than all of theplurality of pores 220 may be etched. As shown, for example, some of thepores 220 may not be etched while other pores 220 are etched to form therecess 222.

The recess 222 shown in FIG. 4 may be a trench or a blind hole in thesubstrate 210 or the recess 222 may be formed through an entirethickness of the substrate 210 to form a through-hole, as shown in FIG.5. The substrate 210 including the recess 222 may form, at least inpart, a MEMS device, a printhead, or another device. In various ones ofthese implementations, a printhead may be formed with the MEMS device.

In various implementations, a substrate may be etched on oppositesurfaces for forming a device. As shown in FIG. 6, a method for etchinga substrate 610 may include sputtering metal catalyst layers 618 a, 618b onto the first surface 616 of the substrate 610 and on the secondsurface 624 of the substrate 610, as shown in FIG. 6. The substrate 610may be etched using a solution that reacts with the metal catalyst layer618 a, 618 b to form a plurality of pores 620 a, 620 b in each surfaceof the substrate 610, as shown in FIG. 7.

After etching the substrate 610 to form the plurality of pores 620 a,620 b, the substrate 610 may be etched to remove at least some of theplurality of pores 620 a, 620 b to form at least one recess 622 a, 622 bin each surface of the substrate 610, as shown in FIG. 8. In variousimplementations, all or fewer than all of the plurality of pores 620 a,620 b may be etched. As shown, for example, some of the pores 620 a, 620b may not be etched while other pores 620 a, 620 b are etched to formthe recesses 622 a, 622 b.

As shown, at least one of the recesses 622 a in the first surface 616 ofthe substrate 610 may interconnect with at least one of the recesses 622b in the second surface 624 of the substrate 610, as shown in FIG. 8.Other ones of the recesses 622 a, 622 b may comprise a trench, a blindhole, another opening, or a combination thereof. The substrate 610including the recesses 622 a, 622 b may form, at least in part, a MEMSdevice, a printhead, or another device. In various ones of theseimplementations, a printhead may be formed with the MEMS device.

By patterning the substrate 610 on both surfaces 616, 624, more complexdevices may be formed or may be formed with fewer separate operationsthan by patterning the substrate 610 on only one surface. In variousimplementations, the substrate 610 may comprise multiple substratelayers such as, for example, a silicon substrate bonded to anothersilicon substrate. The substrate layers may comprise substrates of thesame or different crystal orientation. For example, the substrate 610may comprise two <100>, <110>, or <111> substrates bonded together, andthe substrates may be arranged so the crystal orientations align or areoffset. In some implementations, the substrate 610 may comprisesubstrates of different crystal orientations. For example, the substrate610 may comprise a <100> substrate bonded with ϵ<110> substrate, or someother combination of crystal orientations.

Various aspects of the illustrative embodiments are described hereinusing terms commonly employed by those skilled in the art to convey thesubstance of their work to others skilled in the art. It will beapparent to those skilled in the art that alternate embodiments may bepracticed with only some of the described aspects. For purposes ofexplanation, specific numbers, materials, and configurations are setforth in order to provide a thorough understanding of the illustrativeembodiments. It will be apparent to one skilled in the art thatalternate embodiments may be practiced without the specific details. Inother instances, well-known features are omitted or simplified in ordernot to obscure the illustrative embodiments.

Flow diagrams are provided to describe various methods for etching asubstrate, in accordance with various implementations. While the flowdiagrams illustrate various operations in a particular order, thedrawings are not intended to limit the present disclosure to anyparticular order. Additionally, the drawings are not intended to implythat all operations are required for all implementations.

The phrases “in an example,” “in various examples,” “in some examples,”“in various embodiments,” and “in some embodiments” are used repeatedly.The phrases generally do not refer to the same embodiments: however,they may. The terms “comprising,” “having,” and “including” aresynonymous, unless the context dictates otherwise. The phrase “A and/orB” means (A), (B), or (A and B). The phrase “A/B” means (A), (B), or (Aand B), similar to the phrase “A and/or B”. The phrase “at least one ofA, B, and C” means (A), (B), (C), (A and B), (A and C), (B and C), or(A, B and C). The phrase “(A) B” means (B) or (A and B), that is, A isoptional. Usage of terms like “top”, “bottom”, and “side” are to assistin understanding, and they are not to be construed to be limiting on thedisclosure.

Although certain embodiments have been illustrated and described herein,it will be appreciated by those of ordinary skill in the art that a widevariety of alternate and/or equivalent embodiments or implementationscalculated to achieve the same purposes may be substituted for theembodiments shown and described without departing from the scope of thisdisclosure. Those with skill in the art will readily appreciate thatembodiments may be implemented in a wide variety of ways. Thisapplication is intended to cover any adaptations or variations of theembodiments discussed herein. It is manifestly intended, therefore, thatembodiments be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A method comprising: sputtering first islands ofa metal catalyst onto an un-patterned, unmasked flat face of asubstrate; sputtering second islands of the metal catalyst onto theunpatterned, flat face of the substrate, the second islands beingdifferent than the first islands in at least one of inter-island spacingand individual island size; forming a first plurality of pores in thesubstrate corresponding to the first islands and a second plurality ofpores in the substrate corresponding to the second islands by exposingthe substrate to a solution that reacts with the first islands and thesecond islands of the metal catalyst; and forming a recess in thesubstrate by etching the substrate to remove the first plurality ofpores.
 2. The method of claim 1, wherein the metal catalyst comprises ametal selected from a group consisting of gold, silver, platinum,ruthenium, platinum, palladium, molybdenum, chromium, copper, tantalum,titanium, tungsten, and alloys thereof.
 3. The method of claim 1,wherein said sputtering of the first islands and said sputtering of thesecond islands is performed at a power in a range of about 50 W to about200 W for a time in a range of about 5 seconds to about 60 seconds. 4.The method of claim 1, wherein the solution comprises hydrogen peroxide,hydrofluoric acid, and water.
 5. The method of claim 1, wherein saidetching, by which the recess in the substrate is formed from the removalof the first plurality of pores, comprises performing an isotropic etchof the substrate.
 6. The method of claim 1, wherein said etching, bywhich the recess in the substrate is formed from the removal of theplurality of pores, comprises performing an anisotropic etch of thesubstrate to remove the first plurality of pores to form the recess inthe substrate.
 7. The method of claim 1, wherein said etching comprisesbulk etching the substrate using tetra-methyl ammonium hydroxide,potassium hydroxide, hydrofluoric acid, or nitric acid.
 8. The method ofclaim 1, wherein the recess comprises a through-hole.
 9. The method ofclaim 1, wherein the recess has a width of at least 1 um.
 10. The methodof claim 1, wherein the recess has a width in a range of about 10 um toabout 20 um.
 11. The method of claim 1, wherein the substrate comprisessilicon.
 12. The method of claim 1, wherein said etching of thesubstrate is carried out to maintain the second plurality of pores. 13.The method of claim 1, wherein the first face is an unpatterned flatface continuously extending in a single plane from a first edge to asecond opposite edge of the substrate.
 14. The method of claim 1,wherein each of the first islands and the each of second islands haveunopposed sides immediately following the sputtering.
 15. A methodcomprising: sputtering a first layout of first islands of a metalcatalyst onto a first face of a substrate; sputtering a second layout ofsecond islands of the metal catalyst onto a second face of thesubstrate, the second face extending opposite the first face, whereinthe first layout partially overlaps the second layout; forming a firstplurality of pores in the substrate corresponding to the first islandsand a second plurality of pores in the substrate corresponding to thesecond islands by exposing the substrate to a solution that reacts withthe first islands of the metal catalyst and the second islands of themetal catalyst; forming a first recess in the first face of thesubstrate by removing the first plurality of pores by etching thesubstrate; and forming a second recess in the second face of thesubstrate by removing the second plurality of pores by etching thesubstrate, wherein the first recess and the second recess partiallyoverlap one another.
 16. The method of claim 15, wherein the substratecomprises at least a portion of a printhead.
 17. The method of claim 15,wherein the first face is an unpatterned flat face continuouslyextending in a single plane from a first edge to a second opposite edgeof the substrate.
 18. The method of claim 15, wherein each of the firstislands and the each of second islands have unopposed sides immediatelyfollowing the sputtering of the first layout of first islands and thesecond layout of second islands.